SLPI and chronic kidney disease: To identify the key markers associated with RIF, we performed LASSO regression analysis with those 17 IRGs for the GSE12682 dataset, which contained 23 CKD samples with evidence of tubulointerstitial fibrosis and 13 healthy control samples, and finally identified six IRGs in the model: apolipoprotein H (APOH), epidermal growth factor (EGF), lactotransferrin (LTF), lysozyme (LYZ), phospholipid transfer protein (PLTP), and secretory leukocyte peptidase inhibitor (SLPI) (Figures 2C, D).